1. Field Of The Invention
The present invention relates to a downhole tool for use in oil or gas wells, or the like. This tool is constructed to perform what is known as a "well surging operation" where formation fluid from a zone of the well is rapidly surged out of the formation and into the well to clean debris away from the inner surfaces of the formation and to clean debris from perforations in the well.
2. Description Of The Prior Art
The prior art includes systems for performing surging operations on a well. These prior art systems generally utilize either rupture discs or flapper-type valves to rapidly replace the producing formation in communication with a low pressure chamber in the tool, so that fluid from the formation will rapidly flow into the tool.
The most commonly used prior art system includes a rupture disc which is ruptured by the thrusting action of a plunger.
Although these prior art techniques produce a dynamic surging effect and acceptable drawdown of the producing formation of the well, the pieces of the disc itself will sometimes clog choke valves and other equipment connected to the well after the disc is ruptured. Such a condition most often occurs when the disc does not shatter into fine enough pieces to be circulated out of the well.
Another unfavorable condition that sometimes occurs with these prior art systems is when the disc itself does not completely detach, and instead acts somewhat as a flapper valve in the inner bore of the drill pipe. Under that circumstance, difficulties are presented in circulating fluid upward through the drill pipe, due to the flapper valve effect of the partially severed ruptured disc. In such situations, the less desirable method of circulating fluids up through the well annulus has to be utilized.
Additionally, the materials, such as aluminum, from which the rupture discs are often constructed are not totally reliable when utilized in corrosive environments. Actions of corrosives weaken the rupture discs and quite often operators experience premature rupturing of the disc.
Thus, there has been a need in the prior art for a well surging system which could provide rapid communication of the well zone with the low pressure chamber, so as to achieve the required rapid surging of fluid from the well zone into the low pressure chamber, and yet avoiding the various problems pointed out above with rupture disc type systems.